Metal product incorporating molybdenum disulphide and method and additive for produciing the same



nited States METAL PRODUCT lINCQRPORATING MOLYB- DENUM DISULPHIDE AND METHOD AND ADDITIVE FOR PRODUCING THE sAm Edgar c. Wallace, Watertown, N. r.

' N Drawing. Application June 8,1956, Serial No. 5%,107

8 Claims. (Cl. 75-133 molybdenum enters into the steel matrix to form :an

alloy therewith while the sulphur unites with the manganese in the steel and forms manganese sulphide, the decomposition of the molybdenum disulphide rapidly proceeds to completion. While molybdenum disulphide has excellent lubricating characteristics, molybdic oxide and manganese sulphide do not so that the lubricating value of the molybdenum disulphide additive is vitiated when added to the melt.

In order to fully utilize the lubricating value of the molybdenum disulphide, it is necessary to prevent easy dislodgment of the molybdenum disulphide particles from the surface thereof. The plain molybdenum disulphide will not unite with the metallic body, but will instead remain in the form of small occlusions therein. These occlusions, when exposed on the surface of the body during machining or grinding, will be easily dislodged. The ready dislodgment and removal of the molybdenum disulphide particles from the surface of the body materially reduces the efficiency of the molybdenum 4 disulphide as a lubricant during machining and grinding and also during subsequent use of the body.

In accordance with the present invention, the molybdenum disulphide powder is treated, before addition to :a metallic mixture and solidification thereof into a solid 'body, in such a manner as to prevent or retard decomposition of the molybdenum disulphide and the oxidation thereof to molyb-dic oxide and to also improve the "bond between the molybdenum disulphide particles and the metallic body to prevent easy dislodgment of the molybdenum disulphide from the surface of the body during machining and use.

An important object of this invention is to improve :the bond between the molybdenum disulphide particles :and the metallic body to which it is added to inhibit disllodgment of the molybdenum disulphide particles from the surface of the body and thereby improve the machinability and grindability of the body as well as the wear characteristics thereof.

Another object of this invention is to prevent the partial or complete oxidation of molybdenum disulphide to molybdic oxide when incorporating the molybdenum disulphide into a solid metallic body.

A further object of this invention is to inhibit the decomposition of molybdenum disulphide which tends to occur when'the molybdenum disulphide powder isheated 'by addition to a metallic-melt.

ate

f 'atented Apr. 30, 1957 'ice In accordance with the present'invention molybdenum disulphide is treated, before addition to a metallic mix ture and solidification of the mixture into a solid body, to provide a heat resistant metallic coating on the molybdenum disulphide particles. This inhibits oxidation of the molybdenum disulphide to molybdie oxide which destroys the lubricating value of the molybdenum disulphide, inhibits decomposition of the molybdenum disulphide, and also functions to increase the bond between the molybdenum disulphide particles and the metallic body since the metallic coating blends with the body and more firmly locks the molybdenum disulphide particles thereto.

The formation of a metallic coating on the molybdenum disulphide particles is advantageously effected by partially reducing finely comminuted molybdenum disulphide to provide a coating of metallic molybdenum on the surface. While molybdenum disulphide starts to oxidize in the presence of excess air at about 900 F., metallic molybdenum does not begin to oxidize until the temperature reaches around 2000 F. Therefore, the

, coating of metallic molybdenum on the molybdenum disulphide particles inhibits the oxidation of the molybdenum disulphide and does not itself readily oxidize so that the formation of molybdic oxide is eifectively prevented.

Although the molybdenum disulphide tends to decompose into molybdenum and sulphur when heated by addition to the molten metal, this reaction is reversible. The presence of the metallic molybdenum coating on the molybdenum disulphide particles provides an excess of molybdenum which tends to force the molybdenum and the sulphur back into combination and thus inhibit decomposition of the molybdenum disulphide.

in the preferred form of carrying out the invention, dry molybdenum disulphide powder is spread out on a ceramic tray in a thin layer and arranged to provide. a large surface area. The powder is preferably finer than 400 mesh to provide proper dispersion of the powder in the metallic mixture and after being spread out on the tray may be criss-crossed with a spatula to provide a large exposed surface area. The molybdenum disulphide is then heated in a reducing atmosphere to its decomposition temperature for a time suflicient to reduce the surface portion only of the molybdenum particles to provide a layer of metallic molybdenum thereon, the thickness of which layer is preferably such that the metallic molybdenum comprises about 15 percent of the volume of the particle. Preferably, the heating is done in an atmosphere furnace having a reducing atmosphere such as dissociated ammonia supplied thereto from an external dissociator. The rate of heating and cooling of the molybdenum disulphide particles is not critical but the reducing gas must be on during the heating and until the molybdenum disulphide has been cooled to at least 500 F. in order to effect partial reduction of the molybdenum disulphide the powder is preferably heated to a temperature above 1850 F., at which temperature negligible reduction occurs, and below 2050 F., at which temperature the molybdenum disulphide particles are substantially completely reduced to metallic molybdenum.

particles thereto.

When the molybdenum disulphide is heated to a temperature of about 1950" F., plus or minus F., the time of heating must be about two hours, less time being necessary at higher temperatures and more time being necessary at lower temperatures. When the molybdenum disulphide. powder'is treated in this manner, the sulphur loss at the surfaces of the particles is approximately 10 to The interior of. the particles is substantially unchanged molybdenum disulphide, and the outer surface is reduced to substantially metallic molybdenum, as determined by X-ray and metallographic studies of the treated particles.

The molybdenum disulphide powder, after being treated, is maintained out of contact with contaminating influences and particularly oxygen. When the molybdenum disulphide is to be added to a molten melt such as steel,

the treated powder may conveniently be placed in a :tightly shut metallic box of thin gauge and formed of .steel or ferrous metal.

The molybdenum disulphide may conveniently be added to cast metal bodies by placing the boxes containing the treated molybdenum disulphide in the pouring laddle during the teeming period and after complete de-oxidation has taken place and immediately before ingot pouring. Alternatively, the treated molybdenub disulphide powder may be added to the pour stream as -it emerges from the pouring laddle. After solidification into a solid ingot, the latter is then handled in the customary manner including soaking, cogging, roll- 'coating' which is firmly bonded to the molybdenum disulphide'particles and which will blend with the metal of the solid metallic body to firmly bond the treated This materially enhances the strength of the metallic body containing the molybdenum disuljphide particles and prevents ready dislodgment of the molybdenum disulphide particles from the surface of the body during machining and grinding. Consequently, the treated molybdenum disulphide particles tend to remain at the surface of the body during grinding and machining for a relatively longer period than to untreated molybdenum disulphide particles so that the lubrication value of a given quantity of molybdenum disulphide in the metallic body is materially improved. Moreover since the treated molybdenum disulphide particles tend to remain on the surface of the body, they improve the wear characteristics of the metal during use. advantageous in the formation of cutting tools and the like of materials which are hard to grind since it not only reduces the wear on the grinding wheel and reduces the temperature rise in the article being ground,

but also serves as a lubricant during use of the cutting tool to improve the life thereof. Molybdenum disulphide may also be advantageously added to relatively softer metals in which machining and grinding are not serious problems,

since the molybdenum disulphide is effective as a lubricant to reduce wear between relatively moving parts.

The amount of molybdenum disulphide added to the metallic mixture may vary. However, when incorporating the molybdenum disulphide into steel, the included sulphur content of the partially reduced molybdenum disulphide powder should'be at least .l% to provide any appreciable lubricating characteristic. The maximum including sulphur content should be approximately .35 in steel since the addition of the treated molbdenum disulphide to provide an included sulphur content in the steel in excess of the above limits tends to render the material hot short and the steel tends to crack up during rolling. The addition of the treated molybdenum disulphide powderto various different steels produced measurable improvements, in the machinability, grindability, and

This is highly r 4 wearability thereof, as is apparent from the following specific examples.

(a) On a -50 carbon alloy steel, the machinability of the steel having the treated molybdenum disulphide powder added thereto was improved by a factor of 50% to 100% over that of the same alloy steel which did not have the treated molbdenum disulphide added thereto.

(b). The temperature of grinding gear cutting hobs formed of M-2 high speed steel and containing'treated molybdenum disulphide was reduced so that the hobs did not take on a brown to blue discoloration which is usual for 32 diametral pitch hobs. Moreover, the tool life of these hobs was improved by in a comparison cutting operation with hobs formed of the same high speed steel and which did not contain treated molybdenum disulphide.

(0) M-3 high speed steel containing molybdenum disulphide ground cooler. by a factor of less heat as measured by surface temperature rise than did regular resulphurized M-3 high speed steel. The grinding wheel was not loaded in grinding the M-3 high speed steel containing molybdenum disulphide While the grinding wheel was slightly loaded in grinding the regular M3 steel. The surface of the steel containing molybdenum disulphide was flat after grinding, as noted by rubbing on a cast iron lap pattern,while the regular M-3 steel was considerably warped, due to the aforementioned heating during grinding.

These experiments indicate that tools formed of tool steels in general can be produced with greater economy because of the improved machinability and grindability imparted thereto by the molybdenum disulphide and that hard to grind tool steels could be satisfactorily ground without excessive temperature rises. Moreover, the wearability of materials is also materially enhanced.

Since the coating of metallic molybdenum on the surface of the molybdenum disulphide particles blends more readily with the metallic mixtures, the treated molybdenum disulphide can also be advantageously incorporated in sintered metallic bodies such as carbides and the like. The molybdenum disulphide powder is treated as hereinbefore described by reducing the surface portion only to metallic molybdenum and the treated molybdenum disulphide then added to the powdered mixture before sintering of the latter into a solid body. At the temperatures and pressures involved in sintering the metallic body, the metallic molybdenum coating on the molybdenum disulphide particles blends with the base metal and provides improved strength and an improved bond between the molybdenum disulphide powder and the base metal so that ready dislodgment of the molybdenum disulphide powder from the sintered body is inhibited.

Iclaim:

1. The method of making a solid metallic body containing molybdenum disulphide comprising forming a metallic coating on the surface of finely divided molybdenum disulphide powder, mixing the coated molybdenum disulphide powder with a metallic mixture, and forming the metallic mixture into a solid body.

2. The method of incorporating molybdenum disulphide in a solid metallic body comprising reducing the surface portion only of finely divided molybdenum disulphide powder to produce a thin coating of metallic molybdenum around each particle, and adding the partially reduced molybdenum disulphide powder to a metallic mixture before solidification of the mixture into a solid body.

3. The method of incorporating molybdenum disulphide in a solid metallic body comprising heating finely divided molybdenum disulphide powder in a reducing atmosphere to its decomposition temperature until the surface portion only of the molybdenum disulphide particles .has been reduced to metallic molybdenum, and adding the partially reduced molybdenum disulphide powder to a metallic mixture before solidification of the mixture into a solid body.

4. The method of incorporating molybdenum disulphide in a solid metallic body comprising heating finely divided molybdenum disulphide powder to about 1950 F. in a reducing atmosphere of dissociated ammonia, maintaining the powder at that temperature and in the reducing atmosphere until the surface portion only of the molybdenum disulphide particles is converted to metallic molybdenum, and adding the partially reduced molybdenum disulphide powder to a metallic mixture before solidification of the mixture into a solid body.

5. The method of making steel comprising reducing the surface portion only of finely divided molybdenum disulphide powder to produce a thin coating of metallic molybdenum around each particle, adding the partially reduced molybdenum disulphide powder to the melt after complete deoxidation of the melt, in proportions to provide an included sulphur content in the range of .1% to .35 and solidifying the melt.

6. An additive for use in metallic mixtures to improve 1 6 the machinability and lubricity thereof comprising finely divided molybdenum disulphide powder having a metallic coating of molybdenum completely surrounding each particle.

7. An additive for use in metallic mixtures to improve the machinability and lubricity thereof comprising finely divided molybdenum disulphide powder having the surface portion only thereof reduced to pure molybdenum to provide a metallic coating completely surrounding each particle of molybdenum disulphide.

8. A metallic body having improved machinability and lubricity comprising finely divided molybdenum disulphide powder having a metallic coating of molybdenum completely surrounding each particle and dispersed in the matrix of said metallic body.

Kissock July 28, 1925 Lucas Aug. 14, 1925 

1. THE METHOD OF MAKING A SOLID METALLIC BODY CONTAINING MOLYBDENUM DISULPHIDE COMPRISING FORMING A METALLIC COATING ON THE SURFACE OF FINELY DIVIDED MOLYBDENUM DISULPHIDE POWDER, MIXING THE COATED MOLYBDENUM DISULPHIDE POWDER WITH A METALLIC MIXTURE, AND FORMING THE METTALIC MIXTURE INTO A SOLID BODY. 